1. Field of the Invention
The present invention relates to a retaining fastener wherein a plurality of protrusions having retaining heads provided to a one sheet are retained to a the other sheet, and to disposable diapers and the like using this retaining fastener; and particularly to a retaining fastener wherein the retaining strength of the one sheet and the other sheet has been improved, and to diapers using this fastener.
2. Description of the Prior Art
Regarding the type of disposable diapers generally referred to as "open-type" diapers, the front part and rear part are formed continuously so as to be foldable in two. In use, the rear part is applied to the baby's rump and the front part is passed across the crotch and applied to the side of the abdomen. Next, wing-like formations on either side of the rear part are retained to an exterior sheet on the front part. As for means for retaining the aforementioned wing-like formations to the surface of the front side, an arrangement using retaining fasteners has been suggested.
As shown in FIG. 7, this retaining fastener is comprised of a one sheet 1 and an other sheet 2. The one sheet 1 is formed of a resin material, and is comprised of a base sheet 1a and protrusions 3 arrayed in order over the entire surface of this base sheet 1a, with retaining heads 3a being integrally formed on the tip of these protrusions 3. The overall form of the protrusion 3 and the retaining head 3a is a T-shaped or J-shaped form. The other sheet 2 is comprised of a plurality of loops 4 of filaments formed on a base material 2a, or the entirety is formed of man-made woven fabric or non-woven fabric, or the like.
What is required of retaining fasteners to be used for disposable diapers and the like is that the item be inexpensive and at the same time be able to exhibit a certain degree of retaining strength; woven fabric or non-woven fabric used as the other sheet is preferably used to satisfy these conditions. Also, it is preferable that the form of the retaining heads 3a of the one sheet 1 be of a T-shaped or mushroom-shaped form so as not to stimulate the skin upon contact.
However, what is most required of a retaining fastener regarding the function thereof is the retaining strength between the one sheet and the other sheet. If the retaining strength is weak, in the event that the retaining fastener is used for diapers, movement of legs may cause the one sheet and the other sheet to become separated one from another, resulting in the front part and rear part of the diaper shifting in position or coming loose from the body of the wearer, thus allowing for possible leakage of waste.
In order to improve this matter, Japanese Utility Model Provisional Publication No. H4-56008 discloses art wherein a fiber with a great many of loop and coil tangles is mixed into non-woven fabric used as the other sheet, thus facilitating easy hooking of the retaining heads of the one sheet to the other sheet. Also, disclosed in International Patent Publication No. WO 92/20251 is art wherein the ratio between the area of the joining portions between fibers of the non-woven fabric used as the other sheet and the area of the joining portions of the non-woven fabric and packing is made to be a ratio within acertain range; thus securing a wide area capable of causing retaining between the other sheet and the retaining heads of the one sheet.
However, even if such known retaining fasteners are used, there is a limit to the extent to which the retaining strength can be raised. There reason thereof is that with retaining fasteners, e.g., as shown in FIG. 7, not necessarily all of the protrusions 3 of the one sheet 1 are retained by the other sheet 2. In other words, since the one sheet 1 and the other sheet 2 are adhered one to another at a generally uniform pressure over the entire area thereof, some of the protrusions 3 only deform in a retracting direction, and thus the retaining heads 3a thereof cannot enter into the loops 4 of the other sheet 2 or opening space (gaps) between fibers of the woven fabric or non-woven fabric, and as a result, the retaining heads 3a and the loops 4 of the other sheet 2 or the fibers do not be hooked enough.